Controlled-release therapeutical systems (based on a matrix) for the transdermal administration are prepared by incorporation of an active ingredient (active principle) in a polymeric matrix, which acts both as adhesive and “container” for the medicament.
For this reason, a polymeric matrix must satisfy a series of specific requirements:                ability to dissolve the active principle at the desired concentrations;        absence of chemical interactions with the active principle, so as to avoid degradation or alteration;        ability to allow the diffusion of the active principle towards the corneous layer;        absence of irritation or erythema at the application site;        ability to ensure adhesion of the system to the skin during the whole treatment period.        
The matrices are made from solutions of adhesive polymers also referred to as “pressure sensitive adhesives”.
The most commonly used polymers are of acrylic type and are commercially available in the form of powders, granules, aqueous or solvent solutions.
In general, the polymers used for pharmaceutical formulations belong to two classes, those with a glass transition temperature (Tg) higher than room temperature (or use temperature) and those with a Tg lower than room temperature. The former need plasticizers to be used in the formulation of transdermal patches, while the latter can be used as such, since they already have a soft consistency. For this reason, polymers with a Tg <room T are preferred, even if, due to their properties, they are commercialised dissolved in organic solvents.
Many of these polymers are copolymers of acrylic or methacrylic acid and/or esters thereof, therefore the polymer chains contain acidic functions which can interact with the active principle causing oxidation and/or degradation of the active principle.
It has now been found that matrix-based therapeutical systems for the controlled release of medicaments can be prepared by suitably salifying the free carboxy groups of the polymer chains of macromolecules mixtures having a lower Tg.